FIG. 1 is a block diagram of a conventional system 100 for maintaining a pressure within a transfer chamber 102 of a semiconductor device manufacturing tool (e.g., the Endura™ (shown in FIG. 4) or the Centura™, both manufactured by Applied Materials, Inc.). The transfer chamber 102 is shown coupled to a first load lock 104 and to a second load lock 106. The load locks 104, 106 are adapted to transfer semiconductor wafers to and/or from the transfer chamber 102 as is well known in the art.
With reference to FIG. 1, to employ the conventional system 100 to maintain a pressure within the transfer chamber 102, a user (not shown) supplies a user defined input 108 to a mainframe controller 110 of the conventional system 100 (e.g., a conventional fabrication controller such as a manufacturing execution system (MES)). The user defined input 108 represents a pressure at which the transfer chamber 102 is to operate (e.g., a set point pressure for the transfer chamber 102).
To maintain the set point pressure within the transfer chamber 102, the conventional system 100 employs a mass flow controller 112 to adjust a flow rate of nitrogen (or some other inert, non-reactive gas supplied from a regulated gas supply 114) into the transfer chamber 102 and employs a throttle valve 116 to adjust a rate at which the nitrogen (and any other impurities such as oxygen that are out-gassed from the chamber walls) is pumped from the transfer chamber 102 (via a vacuum pump 118). Accordingly, after receiving the user defined input 108, the mainframe controller 110 employs an algorithm to (1) calculate a flow rate of nitrogen into the transfer chamber 102 (e.g., by calculating a flow rate set point for the mass flow controller 112); and (2) calculate a pump rate of nitrogen (and any other gases) from the transfer chamber 102 (e.g., by calculating a throttle valve position control signal for the throttle valve 116). The flow rate set point and the throttle valve position control signal are provided from the mainframe controller 110 to the mass flow controller 112 and to the throttle valve 116, respectively, as shown in FIG. 1.
The mainframe controller 110 provides a pneumatic control signal to a first isolation valve 120 so as to open the first isolation valve 120 and allow nitrogen to flow from the regulated gas supply 114 through the mass flow controller 112 and into the transfer chamber 102 via a nitrogen filter 122 (e.g., a Millipore distributed by U.S. Filter, Inc.); and the mainframe controller 110 provides a pneumatic control signal to a second isolation valve 124 so as to open the second isolation valve 124 and allow the vacuum pump 118 to pump the transfer chamber 102.
After establishing the flow rate of the mass flow controller 112 and the position of the throttle valve 116, the mainframe controller 110 employs a first pressure transducer 126 (e.g., an MKS Instruments' capacitive manometer, a Baratron capacitive manometer, a Granville Philips' convection gauge, etc.) coupled to the transfer chamber 102 to monitor the pressure within the transfer chamber 102 (e.g., by periodically sampling the output signal of the first pressure transducer 126). Based on each sampled output signal of the first pressure transducer 126, the mainframe controller 110 recalculates a flow rate set point for the mass flow controller 112 and a throttle valve position control signal for the throttle valve 116 (to adjust the flow rate of nitrogen into the transfer chamber 102 and/or the pump rate of gas from transfer chamber 102) so as to achieve the pressure originally defined by the user defined input 108. Note that some conventional throttle valves may include a local controller for monitoring chamber pressure and adjusting throttle valve position based thereon.
When pressure variations result in the transfer chamber 102 (e.g., due to the opening of the first load lock 104 when a wafer is transferred into the transfer chamber 102 from the first load lock 104, the opening of the second load lock 106 when a wafer is transferred out of the transfer chamber 102 to the second load lock 106, and/or when a processing chamber (not shown) coupled to the transfer chamber 102 is opened to transfer a wafer to or from the processing chamber), the mainframe controller 110 detects the pressure change via the first pressure transducer 126 and accordingly adjusts one or both of the flow rate of the mass flow controller 112 and the position of the throttle valve 116. The conventional system 100 thus employs a feedback control loop comprising the first pressure transducer 126, the mainframe controller 110, the mass flow controller 112 and the throttle valve 116 to maintain the desired pressure within the transfer chamber 102.
To control the pressure in the first load lock 104 and the second load lock 106, the conventional system 100 employs a separate vacuum pump 128 coupled to the first load lock 104 via a second isolation valve 130 and coupled to the second load lock 106 via a third isolation valve 132. Both isolation valves 130, 132 are controlled by pneumatic control signals from the mainframe controller 110 and may be individually opened/closed to selectively evacuate each load lock. Similarly, a regulated nitrogen flow may be provided to each load lock 104, 106 via a regulated nitrogen supply 134 coupled to both the first load lock 104 and the second load lock 106 via an isolation valve 136 and an isolation valve 138, respectively. The pressure within the first load lock 104 is measured by the mainframe controller 110 via a second pressure transducer 140 and the pressure within the second load lock 106 is measured by the mainframe controller 110 via a third pressure transducer 142. Note that an isolation valve 144 that is controllable by the mainframe controller 110 also is provided between the regulated gas supply 114 and the filter 122 (e.g., so as to allow the mass flow controller 112 to be bypassed if desired).
The conventional system 100 of FIG. 1 suffers from a number of drawbacks. For example, the mainframe controller 110's empirical calculation of both a flow rate for the mass flow controller 112 and a throttle valve position for the throttle valve 116 based on a measured pressure within the transfer chamber 102 is a complex calculation that (1) is not highly accurate (e.g., as the method by which a mass flow controller measures mass flow is prone to error unless repetitive calibration is used); and (2) may be time consuming to implement because the mainframe controller 110 may need to control numerous other functions (e.g., the operation of the first load lock 104, of the second load lock 106, of various processes and processing chambers (not shown) coupled to the transfer chamber 102, etc.) and because of the slow response time of the throttle valve 116. Accordingly, the pressure within the transfer chamber 102 is not highly regulated (e.g., may fluctuate to an unacceptable level for a given period of time). Additionally, the conventional system 100 is expensive because of the use of a throttle valve (e.g., the throttle valve 116) and a mass flow controller (e.g., the mass flow controller 112), and because of the use of a separate pump (e.g., the vacuum pump 128) to control the pressure within first load lock 104 and the second load lock 106.
Accordingly, a need exists for improved methods and apparatus for maintaining a pressure within a vacuum chamber such as a transfer chamber of a semiconductor device manufacturing tool.